But the company must still demonstrate its approach will ensure safety before those planes can fly again, the FAA said on Tuesday in signing off on a certification plan by the world's biggest aircraft manufacturer to redesign the plane's lithium-ion battery system.

"The certification plan is the first step in the process to evaluate the 787's return to flight and requires Boeing to conduct extensive testing and analysis to demonstrate compliance with the applicable safety regulations and special conditions," the FAA said in a statement.

Boeing's newest and most advanced commercial jetliner was grounded in January by regulators worldwide after two battery-related fires damaged 787s in Boston and in Japan. No passengers or crew were hurt in either incident.

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There are only 50 Dreamliner wide bodies flying worldwide, but Boeing has orders for several hundred more. Fixing the battery problem quickly and definitively is paramount for the company, considering the sizable investment of the industry following the model's problem-plagued development.

"This comprehensive series of tests will show us whether the proposed battery improvements will work as designed," said Transportation Secretary Ray LaHood. "We won't allow the plane to return to service unless we're satisfied that the new design ensures the safety of the aircraft and its passengers."

The layered fix aims to prevent any fires from developing, and Boeing said it was confident in its approach.

Proposed last month, the plan includes a redesign of internal battery components to minimize chances of a short circuit. It also involves better insulation of battery cells and adding a new containment and venting system aimed at preventing any overheating from affecting the plane or being noticed by passengers, Boeing said.

The FAA will approve the redesign only if the company successfully completes all required tests and analysis to demonstrate the new design complies with federal safety requirements.

Ray Conner, president and chief executive officer of Boeing's commercial airplane unit, said in a statement that the company's focus has been on developing a permanent resolution.

"Working with internal and external experts in battery technology, we have proposed a comprehensive set of solutions designed to significantly minimize the potential for battery failure while ensuring that no battery event affects the continued safe operation of the airplane," said Conner.

"We have a great deal of confidence in our solution set and the process for certifying it," said Conner.

The FAA also will permit Boeing to begin test flight activities relating to the battery issue.

The investigation of Dreamliner battery fires has been ongoing in the United States and Japan. The FAA's grounding of the aircraft was recognized by regulatory agencies worldwide.